The present invention relates to spark gap protectors and more particularly to spark gap protectors providing backup protection in case of failure of a main spark gap.
Electrical communications equipment is conventionally provided with a station protector for shorting hazardous overvoltage surges to ground. These overvoltage surges can be caused by lightning strokes, power contact of the communication lines with voltage supply lines, power induction, ground potential rise and static buildup. The station protector typically includes a spark gap having carbon block electrodes disposed between the equipment line and ground, and a heat actuated "failsafe" means for permanently shorting the line to ground after an extended gap discharge renders the gap ineffective for further protection.
Another form of station protector includes a gas tube spark gap device and a permanent shorting means. This gas tube is advantageously employed since it can be designed to spark over at a comparatively low voltage as compared with carbon blocks, thereby offering additional protection. However, the gas tube device can become damaged as the result of an overvoltage condition, while insufficient heat is generated to actuate the "failsafe" permanent shorting means. For example, the normal gas tube spark gap device has a predetermined breakdown voltage, e.g., of a few hundred volts, but if the hermetic seal of the gas tube is broken as the result of a transient overvoltage condition, the breakdown voltage thereof may rise to several thousand volts providing insufficient protection to the line to which the device is connected. The gas tube device is dependent upon its internal gaseous environment for its low breakdown voltage, its electrodes being comparatively widely spaced for enhancing the operating life of the device and for enabling manufacture of the device at a lower cost than would be occasioned if a closer exact spacing had to be maintained.